The present invention relates to a technique for playing back information from recording media, and more specifically, to a technique for accessing desired playback time of the information when the information is recorded on the recording medium by a coding scheme in which playback time length is not proportional to coded data amount.
In recent years, Digital Versatile Disc (hereinafter referred to as xe2x80x9cDVDxe2x80x9d) has been gaining popularity. The recording capacity of DVD is several times greater than that of Compact Disc (hereinafter referred to as xe2x80x9cCDxe2x80x9d). For DVD standard, there are DVD-Video for video/audio playback and DVD-Audio for making a point of audio playback which is added to DVD-Video. In DVD-Audio standard, almost all the information recorded on the disc is used for audio playback.
In DVD-Audio standard, there are two types of methods to record audio data on DVD: Linear PCM and Packed PCM. The two types are the same in that the audio data is coded to generate coded data and is recorded on the DVD. However, in Linear PCM, the playback time is proportional to the coded data amount, whereas in Packed PCM, the playback time is not proportional to the coded data amount. Packed PCM uses characteristics of audio signals to compress and record the compressed information, and varies the coded data amount per time in accordance with the temporal repetition of audio data and/or correlation between channels. At a restricted rate, Packed PCM achieves the sound quality exceeding that of Linear PCM.
In DVD-Audio, for example, when a user wishes to start playback from the desired time such as from the midst of music, not from the head of it, or when a user wishes to play back repeatedly the interval of specific times, the playback apparatus should know at which location on the disc the coded data corresponding to the object time is recorded. The recording position of the coded data that corresponds to the object time can be simply calculated if the time length of audio signal is proportional to the coded data amount as is the case of Linear PCM. However, when the playback time length of the audio signal is not proportional to the coded data amount as is the case of Packed PCM, the recording position of the coded data corresponding to the object time is unable to be simply calculated.
FIG. 5 is a block diagram of the configuration of the conventional playback apparatus. Playback apparatus 50 plays back a disc 1 in which the multimedia data is recorded by a recording scheme with the signal playback length not proportional to the coded data amount. On disc 1, multimedia data and management information are recorded. The management information includes information of the start address of the cell that composes the relevant multimedia data, information of end address (i.e. information of data recorded position), and information on the time required for playing back the relevant multimedia data (playback time information).
Playback apparatus 50 comprises a playback section 2, decoder 3, system controller 41, storage 5, display 6, light receiving section 7, and remote operating section 8. Playback section 2 plays back the multimedia data and management information from disc 1. Decoder 3 decodes the multimedia data and management information of disc I and outputs video signal and/or audio signal. System controller 41 identifies the position of the multimedia data to be played back on disc 1, and orders playback section 2, decoder 3, etc. to play back, decode, etc. of multimedia data from the position. Storage 5 is a memory to which system controller 41 accesses to write and read data. Display 6 is controlled by system controller 41. Remote operating section 8 transmits signals such as infrared signals that correspond to user operation. Light receiving section 7 receives signals such as infrared rays from remote operating section 8.
Once disc 1 is set, system controller 41 controls playback section 2 and plays back management information of disc 1 and allows storage 5 to store the information. When the user operates xe2x80x9cplaybackxe2x80x9dfrom remote operating section 8, system controller 41 recognizes this operation via light receiving section 7, controls playback section 2 based on the management information stored, and plays back disc 1. When the desired time to be searched is indicated from remote operating section 8, system controller 41 recognizes the instruction and allows storage 5 to store the desired time. When the operation to start searching is carried out, searching processing of the desired time as shown in FIG. 6 is executed.
FIG. 6 is a flow chart of the search processing of the desired time in playback apparatus 50 (FIG. 5). When the desired time to be searched is set and search starting operation is carried out from remote operating section 8, search processing is begun. This processing is carried out primarily according to the instructions of system controller 41 (FIG. 5). In Step S61, the coded data start position is substituted in the target position and the process moves to Step S62. Right after the start of processing, the preset access initial start position is substituted as the coded data start position. In step S62, the relevant target position is accessed and the process moves to Step S63. In Step S63, the playback time is read at the relevant target position and process moves to Step S64. In Step S64, determination is made on whether the difference between a time presented by the relevant time information and the desired time is within the permissible range or not, and if it is not within the permissible range, the process moves to Step S65. In Step S65, 1 is added to the value of target position and the process returns to Step S62. The operations from Step S62 to Step S65 are repeated until the difference between a time presented by the relevant time information and the desired time is judged within the permissible range, and when the difference is determined within the permissible range in Step S64, the relevant search is ended as the desired time has been reached.
Playback apparatus 50 (FIG. 5) that carries out this kind of search processing has a problem of excessively many access frequencies and takes time for searching, because playback apparatus 50 (FIG. 5) accesses the coded data successively from the specified start position and repeats the access until it reaches the coded data that corresponds to the signal of the desired time.
The present invention has been made in view of these circumstances, and it is an object of the present invention to search the data that corresponds to the signal of the desired time with fewer access frequencies in playing back the recording medium on which the information is recorded by the recording method where the signal playback time length is not proportional to the data amount of the relevant signal.
The playback apparatus according to the present invention is a playback apparatus comprising a playback section for reading an information unit and management information from a recording medium on which the information unit of audiovisual subject for a user and the management information containing playback time information pertaining to a playback time of the information unit and recorded position information pertaining to a recorded position of the information unit are recorded; an operating section for inputting a desired playback time of the information unit; and a control section for searching the recorded position on the recording medium of the information unit based on the recorded position information read by the playback section and for controlling the playback section to play back the information unit from the recorded position, wherein when the information unit is played back from the desired playback time inputted from the operating section, the control section finds an estimated straight line in which the playback time and data amount are proportional to each other based on the playback time information and the recorded position information, the control section searches an estimated recorded position that corresponds to the desired playback time based on the estimated straight line, calculates an error between an actual playback time of the information unit at the estimated recorded position and the desired playback time, and identifies the estimated recorded position as the recorded position of the information unit on the recording medium that corresponds to the desired playback time when the error is within a specified range, thereby the above-mentioned object can be achieved.
A gradient of the estimated straight line is a ratio of the playback time of the information unit to the data amount.
If the error is beyond the specified range, the control section finds a next estimated straight line at least based on the estimated recorded position and the playback time of the information unit that corresponds to the estimated recorded position, searches the next estimated recorded position that corresponds to the desired playback time based on the estimated straight line, calculates an error between an actual playback time of the information unit at a next estimated recorded position and the desired playback time, and repeats searching until the error is included in the specified range.
The gradient of a next estimated straight line is a ratio of a difference of the actual playback time of the information unit to a difference of the data amount at the most recently obtained two estimated recorded positions.
The playback method according to the present invention is a playback method comprising steps of: reading an information unit and management information from a recording medium on which the information unit of audiovisual subject for a user and the management information containing playback time information pertaining to a playback time of the information unit and recorded position information pertaining to a recorded position of the information unit are recorded; inputting a desired playback time of the information unit; searching the recorded position on the recording medium of the information unit based on the recorded position information read; and
controlling playback to play back the information unit from the recorded position, wherein when the information unit is played back from the desired playback time inputted, the playback method further comprises steps of: finding an estimated straight line in which the playback time and data amount are proportional to each other based on the playback time information and the recorded position information; searching an estimated recorded position that corresponds to the desired playback time based on the estimated straight line; calculating an error between an actual playback time of the information unit at the estimated recorded position and the desired playback time; and identifying the estimated recorded position as the recorded position of the information unit on the recording medium that corresponds to the desired playback time when the error is within a specified range, thereby the above-mentioned object can be achieved.
Said finding the estimated straight line includes calculating a ratio of the playback time of the information unit to the data amount to find a gradient of the estimated straight line.
When the error is beyond the specified range, the playback method includes steps of (a) finding a next straight line at least based on the estimated recorded position and the playback time of the information unit that corresponds to the estimated recorded position; (b) searching the next estimated recorded position that corresponds to the desired playback time based on the estimated straight line; (c) calculating an error between an actual playback time of the information unit at a next estimated recorded position and the desired playback time; and (d) repeating steps (a) through (c) until the error is included in the specified range.
Said finding a next estimated straight line includes a step of calculating a ratio of a difference of the actual playback time of the information unit to a difference of the data amount at the most recently obtained two estimated recorded positions to find a gradient of the next estimated straight line.